Modelling water vapour transport, transpiration and weight loss in a perforated modified atmosphere packaging for feijoa fruits

Abstract

In modified atmosphere packaging (MAP), the transpiration of the fresh product and exchange of water through the polymeric packaging are often not properly considered. This paper presents a mathematical model to describe the evolution in water vapour, O2 and CO2 concentrations in the packaging headspace, the weight loss of the product and the condensation of water in a MAP system with perforations. Transpiration was considered as the sum of water transferred out from the product due to the gain of energy from its respiration process and the difference in water activities between the product and the surrounding atmosphere. Respiration was represented using Michaelis–Menten enzyme kinetics. The gas transfer through the packaging and the perforations was described with Fick equations. The temperature influence on these processes was considered to follow the Arrhenius' law. To experimentally determine the model parameters, feijoa fruits (Acca sellowiana Berg) were stored under different storage conditions: packaging type, relative humidity and temperature. The completed model was subsequently validated in a MAP test by packaging fruits in perforated polypropylene (PP) and polylactic acid (PLA) bags for 13 days at 12 °C and 75% RH. Inside the PP bags, a saturated atmosphere (100% RH) was reached and 1.48% of the initial weight in the packed fruit was lost by day 13, while in the PLA bags, an equilibrium RH of 83% and a fruit weight loss of 3.29% were measured. The prediction capacity of the model was satisfactory, with coefficients of determination (R2) between 0.88 and 0.99 for the different tests.